First-in-Human Evaluation of 18F-Mefway, a PET Radioligand Specific to Serotonin-1A Receptors


Hillmer AT, Wooten DW, Bajwa AK, Higgins AT, Lao PJ, Betthauser TJ, Barnhart TE, Rowley HA, Stone CK, Johnson SC, Mukherjee J, Christian BT

Journal of Nuclear Medicine. 2014 Dec;55(12):1973-9.

Abstract

The serotonin-1A (5-HT1A) receptor is implicated in an array of neurological and psychiatric disorders. Current PET radioligands targeting 5-HT1A receptors have limitations hindering widespread PET studies of this receptor system. The 5-HT1A specific antagonist radioligand N-{2-[4-(2-methoxyphenyl)piperazinyl]ethyl}-N-(2-pyridyl)-N-(trans-4-18F-fluoromethylcyclohexane)carboxamide (18F-mefway) exhibited promising in vivo properties in rhesus monkeys. The goal of this work was to examine the in vivo cerebral binding profile and metabolism of 18F-mefway in humans. Methods: Dynamic 18F-mefway PET data were acquired for six healthy volunteers (4F, 2M; 22-38 years). Scans were initiated with the injection of 192-204 MBq radiotracer and data were acquired for two hours. Venous blood samples were collected and assayed to examine the in vivo metabolism profile of 18F-mefway. To examine the test-retest variability of 18F-mefway, a second PET scan was acquired at least two weeks later for four subjects. Regional binding potentials (BPND) were calculated with MRTM, and voxel-wise BPND maps were calculated with Logan graphical analysis. Regions surrounding the brain were carefully inspected for uptake of radiolabeled species in bone. Results: 18F-Mefway uptake in the brain occurred quickly with peak SUVs of 1.7. Rapid washout in the cerebellum resulted in SUVs of 0.2 at 120 minutes, while regions with specific 5-HT1A binding exhibited retention of radioligand yielding SUVs of 0.4-0.9 at 120 minutes. Rapid metabolism of 18F-mefway was observed, with no detected 18F-fluoride ions in plasma. BPND values of 2.4 were measured in the mesial temporal lobe, with values of 1.6 in insular cortex and 0.7-1.0 in other cortical regions. Stable BPND estimates were obtained using 90 minutes of dynamic data. Average test-retest variability was 8%. No evidence of radioactivity uptake in bone was observed. Conclusion: 18F-Mefway exhibits favorable in vivo properties for serotonin 5-HT1A receptor measurements in humans. The simple radiosynthesis, high specific binding profile, and absence of PET signal in bone make 18F-mefway an attractive radiotracer for PET experiments examining the 5-HT1A receptor in neuropsychiatric disorders and drug intervention.

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